I have an Aero Ektar mounted in a CC-400 recessed board, inside out, so it's now an an outy instead of an inny. It fits my Anniversary Speeds just fine. The little lip doesn't allow the slide to go all the way but it has plenty of grip to hold it. Those cast boards would be easy to grind the lip off, if needed. I use Beseler boards from my 45M enlarger for putting Polaroid MP-4 lenses on my Annies.

My apologies, Nick. Your post made me think about this, so I went and checked my enlarger boards. I do indeed have some that fit my Speed, but here's why - they are about 1/16 of an inch too big all around in their natural state and I had forgotten that I had trimmed a couple down some years ago and attached a mounting ring for a 162mm f/4.5 Raptar. This odd size ring also works for the MP-4 lenses. Ah, senior moments. I have also come up with what might be a GV flat board. I don't have a GV so I can't say for sure. It is silver/grey hammer tone finish on the front and has a number cast on the back - 25631. It has a light trap ridge on the back, different from the Calumet boards and the little bevel on the bottom. It fits my Speeds. I don't know if I could scan a picture of it. I would part with it, as it is an uncommon item and I can always make wooden boards. Leave me a PM.